Dual-voltage transformer switch



E- J. LEHMAN DUAL-VOLTAGE TRANSFORMER SWITCH A ril 6, 1965 3 Sheets-Sheet 1 Filed Dec. 6. 1961 IN V EN TOR. fqyem: J L e/zmazz April 1965 E. J. LEHMAN 3,177,305

DUAL-VOLTAGE TRANSFORMER SWITCH Filed Dec. 6. 1961 5 Sheets-Sheet 2 I; 'IIIIIIIIIIIIIIIIIIIIIIIIII/IIIl/II/II/III INVENTOR.

Eqyene J Lehman 33 April 6, 1965 E. J. LEHMAN DUAL-VOLTAGE TRANSFORMER SWITCH 3 Sheets-Sheet 3 Filed Dec. 6, 1961 INVENTOR. E {yene J 46/922 47: BY

flatorncy' United States Patent Office 3,177,305 DUAL-VGLTAGE TRANSFQRMER SWi'ifiH Eugene J. Lehman, Zanesville, Ohio, assignor to lvieGraw- Edison Company, Miiwauiree, Wis a corporation of Delaware Fiied Dec. 6, 1961, Ser. No. 157,349 1% (Iiaims. (Cl. 260-6) This invention relates to electrical switches and more particularly to improvements in high voltage switch means for changing transformer connections.

It is often desirable to be able to easily change the connections between the windings of an electrical transformer. For example, a winding of a transformer may comprise a plurality of sections, and the voltage rating of the transformer may be varied by changing the connections of the winding sections between series and parallel. Dual-voltage, or series-multiple, switches for transformers are known which allow connecting the winding sections in series or in parallel and thus permit operation of the transformer on either of two voltages, for example on 1200 or 2400 volts. Such dual-voltage switch makes it possible for an electrical power utility to change the transformer from a lower voltage rating to a higher voltage rating and thus eliminate the need for replacing the transformer, if a distribution system is changed over to a higher voltage.

As the kva. and voltage rating of transformers increase, the size of the dual voltage switch also increase in order to obtain sufliciently great creepage paths and arc-over distances to withstand the higher voltages and to carry the greater magnitude of current associated with the increase in kva. Dual voltage switches are usually mounted within the transformer tank under the insulating oil, and it is desirable that such switches be as small as possible to prevent increasing the size of the transformer tank any more than is absolutely necessary. National Electrical Manufacturers Association (NEMA) standards require that such dual voltage switches carry rated current continually and also carry short circuit currents of up to twenty five times rated current for a short interval of time, for example, for two seconds. Dual voltage switches conventionally utilize wiping contacts, and it is di fiicult to obtain sufiiciently high contact pressure with wiping contacts to meet NEMA current carrying standards at the higher kva. ratings.

Dual-voltage switches often have switch position indicating means including a stop exterior of the casing for preventing rotation of the movable contact beyond the switch positions. However, if components of the switch are misaligned, the movable contact may hang up between switch positions even through the external indicating means is against the stop and shows that a switch position has been reached. It is an object of the invention to provide a dual-voltage switch which is much more compact than prior art switches of similar voltage and kva. rating.

It is a further object of the invention to provide a compact dual-voltage switch having sufficiently high contact pressure to carry currents well in excess of the minimum values specified by the National Electrical Manufacturers Association for transformers up to 167 kva. and 18 ki-lovolt rating and yet is operable between positions with minimum torque.

Another object of the invention is to provide a dualvoltage switch which can carry currents equal to or in excess of the design level of the transformer which may approach the current resulting from short circuit on the transformer.

A further object of the invention is to provide a dual- Billfihh Patented Apr. 6, 1fi5 voltage switching means capable of changing voltages in multiples other than integers.

Another object of the invention is to provide such a compact dual-voltage switch having high contact pressure and which is operable with low torque even when ganged with a slave switch.

it is a further object of the invention to provide an improved compact dual-voltage transformer switch which provides high contact pressure but relieves the contact pressure while the contacts are being actuated between positions.

Still another object of the invention is to provide a dual-voltage switch which permits overtravel of the operating means after the movable contact has come into engagement with the succeeding stationary contact so that rotational positioning of the operating means is not critical.

A still further object of the invention is to provide a dual-voltage switch wherein alignment and adjustment of the switch components are not critical in order to prevent hanging up of the movable cont-act between switch positions.

These and other objects and advantages of the invention will be better understood from the following detailed description when taken in conjunction with the accompanyin g drawing wherein:

FIG. 1 is a circuit diagram illustrating the switching connections completed by the preferred embodiment of the dual-voltage switch of the invention to alternately connect three transformer winding sections in series and parallel and thus change voltage in a 3 to 1 ratio;

FIG. 2 is a partial vertical section view taken through a distribution transformer having a preferred embodiment of the dual-voltage switch of the invention mounted within the transformer tank;

FIG. 3 is a vertical sectional view taken along line 3-3 of FIG. 5 through the preferred embodiment of the invention;

FIG. 4 is a front view of the preferred embodiment in parallel position with a portion of the movable contact assembly broken away to better illustrate the construction of the stationary contacts;

FIG. 5 is a view similar to FIG. 4 taken along line 55 of FIG. 2 and showing the switch in series position;

FIGS. 6 and 7 are plan views of the preferred embodiment of the invention taken respectively, when the switch is in the normal contact position and in the rotatable position wherein contact pressure is relieved and the cam pin is in driving relation to the movable contact assembly;

FIG. 8 is a circuit diagram of the preferred embodiment of the invention when arranged to alternately connect two transformer winding sections in series and parallel and thus change voltage in a 2 to ,1 ratio;

FIG. 9 is a circuit diagram of dual voltage switching means of the invention adapted to change voltages in multiples other than integers;

FIG. 10 is a side view of a preferred embodiment of dual-voltage switch means of the invention adapted to change voltages in multiples other than whole integers when connected in accordance with the circuit diagram of FIG. 9; and

FIG. 11 illustrates the stop means on an alternative embodiment of the invention.

The series-multiple, or dual-voltage, switch It of the preferred embodiment of the invention illustrated in FIGS. 1 to 7 is adapted when in a first position to connect three transformer primary winding sections AB, CD, and EF in parallel and when in a second position to connect these three winding sections in series in order to change the transformer from a lower voltage to a higher one, or vice versa. The dual voltage switch It) is secured by suitable fastening means 23 to a bracket 11 mounted on a channel upper core clamp 12 which embraces a cruciform-in-cross section yoke 14 of the magnetic core of the transformer. The dual-voltage switch Ml has two sets of three aligned stationary contacts E, A, C, and D, F, B which are individually connected by wire leads 15 to the correspondingly lettered ends of the three transformer primary winding sections AB, CD, and EB so that one end of each coil section is connected to a stationary contact of one set E, A, C and the other end of each coil section and is connected to a stationary contact of the other set D, F, B. For example, end A of winding section AB is connected by a lead 15 to stationary contact A of set E, A, C and end B of this winding section AB is connected by a lead 15 to stationary contact B of set D, F, B. The conductors 16 of an alternating current power system are connected to the stationary contacts A and F.

The movable contact assembly of switch includes a movable member 18 of suitable insulating material having high surface resistivity such as glass-filled alkyd resin and carrying two elongated metallic contacts 19A and 19B in parallel, spaced apart position which are adapted when switch 10 is in the full line parallel position shown in FIG. 1 to respectively electrically common the three stationary contacts E, A, C of one set and the three stationary contacts D, F, B of the other set, whereby the three electrical coil sections AB, CD and EF are connected in parallel.

In the second, or series position of movable member 18 shown in dotted lines in FIG. 1, the elongated metallic contacts 19A and 19B are adapted to respectively common the stationary contacts C and B and the stationary contacts E and D, whereby the three coil sections are connected in series in a circuit which may be traced from one power line lead 16 to winding section AB, stationary contact B, elongated contact 19A, stationary contact C, winding section CD, stationary contact D, elongated contact 319B, stationary contact E, and winding E5 to the other power line lead 116.

A stationary terminal block 21 preferably of suitable molded plastic material such as glass-filled alkyd resin having high surface resistivity carries the six stationary contacts A-F. Terminal block 21 is secured by fastening means 23 to bracket Ill. In order to increase the length of the creepage path and the arc-over distance between adjacent stationary contacts A-F and between the stationary contacts and metallic parts of the transformer, each stationary contact A-F is positioned within a tubular bushing, or contact housing 24 (see FIG. 3) integral with and extending from opposite faces'of terminal block 21. The six stationary contacts A-F are identical and only contact D will be described. Stationary contact D includes a pin 26 having a spherical head 27 thereon and a shank portion 28 which fits within tubular bushing 24 and protrudes through an aperture 31 in terminal block 21 axial of bushing portion 24 and defined by an annular shoulder 33 extending radially inwardly relative to the tubular bushing 24. A helical spring 34 circumjacent shank portion 28 compressed between head 27 and shoulder 33 urges the pin 26 to move in an outward direction, which movement is prevented by a snap ring 36 fitting within a circumferential groove in the end of shank portion 28. The wire lead connecting stationary contact D to Winding section SE is secured to the end of shank portion 28. Helical spring 34 is normally loaded when snap ring 36'engages shoulder 33. Helical spring 34 thus pre-loads contact pin 26 before it is engaged by movable contact 19B and assures that contact D bears against metallic elongated contact 19B with a predetermined minimum pressure. In order to obtain full contact pressure, it is only necessary that the pin 2.6 be moved sufiiciently by elongated contact 19B to disengage the snap ring 36 from the annular shoulder 33. Thus, predetermined contact pressure considerably higher than that obtained by wiping contacts, for example, up to ten pounds for each stationary contact, is provided with minimum axial actuation of the movable contact assembly 18. The relatively large spherical contact heads 27 on the stationary pins-26 help dissipate the heat generated in carrying high currents.

This high and uniform contact pressure, together with the improved heat dissipating characteristics of the spherical head contact pins, permit carrying continually currents well in excess of the values especified in NEMA standards, for example, considerably above the minimum current of 69 amperes for 167 kva. transformers, and also permit carrying short circuit currents of twenty five times this magnitude for two seconds. The design level of transformers established by individual manufacturers usually approaches the current that would result from short circuit on the transformer, and the dual-voltage switch of the invention will carry currents equal to or in excess of such design level and which is substantially above NEMA requirements.

The tubular housings 24 surrounding the stationary contact pin 26 substantially increase the length of the creepage path along the surface of terminal block 21 between adjacent stationary contacts A-F and also between the stationary contacts A-F and metallic parts of the transformer, U-shaped raised portions 38 on both flat faces of terminal block 21 increase the creepage path length and sparkover distance between the stationary contact pins 26 and. the fastening means 23 which secure the terminal block 21 to bracket Ill. The increased creepage path and arc-over distance permit the switch of the invention to withstand without failure the impulse tests required by NEMA standards for transformers of 18 kilovolt rating. The operating shaft id for the dual-voltage switch lltl is preferably of insulating material and extends through an aperture 42 in terminal block 21 located centrally of the stationary contacts AF. A circular flange 43 on the end of operating shaft 4th radially inward of the transformer tank abuts against terminal block 21 and prevents movement of shaft 46 radially outward of the transformer tank. The opposite end of operating shaft 40 is received within an axial compartment 44 in the enlarged diameter end of a stainless steel shaft stub 45. Stub shaft 45 has axially extending slots 46 in diametrically opposed portions thereof which receive a pin 47 extending diametrically through operating shaft 40 to provide a pin-and-slot connection between operating shaft 40 and stub shaft 45, thereby making operating shaft 4t) self-aligning. Stub shaft 45 extends through the sidewall 49 of the transformer tank (see FIG. 2) and is accessible from the exterior of the tank to permit operation of the dual-voltage switch Jltl. Preferably stub shaft 4-5 rotatably extends through a generally tubular metallic bushing 50 having an annular flange portion 51 abutting against the exterior periphery of the tank sidewall 49 and an externally threaded tubular shank portion 52 extending through an aperture in the tank sidewall 4-9 and engaging a nut 54 disposed against the interior of the tank sidewall 49 to clamp bushing 50 to the tank sidewall 49. An O-ring gasket compressed by bushing 519 within a circumferential groove 56 in shaft 45 and an O-ring gasket positioned in an annular groove 58 in flange portion 51 and compressed between the exterior surface of the tank sidewall 49 and flange portion 51 provide a leak-proof seal for stub shaft 45. Movement of stub shaft 45 out of transformer tank sidewall 49 is prevented by the annular shoulder 59 formed by the increased diameter portion on shaft 45 abutting against bushing Stl.

A cylindrical actuating member 60 has an axial compartment for receiving the end of stub shaft 4-5 exterior of the tank sidewall 49. Member 60 is secured by a radially extending pin 61 to shaft 45 and prevents radially inward movement of stub shaft 45. A thin, wedge-shaped.

end 62 is provided on actuating member 6%. A weather proof cap 63*, preferably of aluminum is normally threaded on flange portion 51 to compress an annular gasket against the exterior of tank sidewall 49 and thus provide additional sealing at shaft 435. Cap 63 is formed with a narrow indentation 64 analogous to the slot in a screw and adapted to receive the wedge-shaped end 62 on actuating member 60, when cap 63 is unscrewed, to permit rotation of shafts 4d and 45 when it is desired to operate the dual-voltage switch It.

Movable member 18 of the dual-voltage switch has a central tubular sleeve portion 65 formed with an axial bore 66 which rotatably receives operating shaft 40 and with a spring receiving axial compartment 67. Generally radially extending arm portions 68 integral with sleeve portion 65 support a pair of parallel straight portions 69A and 6913 on opposite sides of sleeve portion 65. Internally threaded metallic inserts 79 (see FIG. 3) molded within the straight portions 6A and 69B engage screws which aflix the elongated metallic contacts 19A and 193 to the straight portions 69A and 693. A pair of stop members 71A and 71B integral with straight portion 69B (see FIG. 4) extend from opposite ends of straight portion 698 parallel to the axis of operating shaft 4th. Stop member 71A abuts against a cooperating stop member 72 on terminal block 21 to position the metallic strip contacts 19A and 19B relative to stationary contacts A-F when the switch is in the parallel position shown in FIG. 4 and in full lines in FIG. 1: similarly stop member 71B cooperates with stop member 72 to position the elongated contacts 19A and MB relative to stationary contacts A-F when the dual-voltage switch It is in the series position illustrated in dotted lines in FIG. 1 and in FIG. 5.

The surface of sleeve portion 65 in a plane radial of operating shaft 40 forms a cam 73 having a pair of diametrically opposed, generally V-shaped depressions 74 with flat raised portions 75 of the cam surface therebetween. A cam pin 76 extending diametrically through the operating shaft 43 rests upon the raised portions 75 of the camming surface 73 between depressions 74 when the dual-voltage switch It is in both the series and in the parallel positions. Uniform and predetermined high pressure contact is assured between the elongated contacts 19A and 19B and the stationary contacts A-F by the compression springs 34 surrounding each stationary contact pin 26 and urging it against the corresponding elongated contact 19A or 19B. Flange 43 on operating shaft 46 prevents axial movement of shaft 40, and cam pin 76 hearing against raised portions 75 of the cam 73 hold the movable member and elongated contacts 19A and BB thereon in the position shown in full lines in FIGS. 2-6 wherein the stationary contact pins 26 compress the helical springs 34- surrounding them against the shoulders 33 sufiiciently to disengage the snap rings 36 from the shoulder 33.

One end of a helical spring 78 surrounding operating shaft 40 extends into axial compartment 67 in movable member 18 and the other end abuts against an annular insulting support 79 surrounding shaft 40 and disposed against terminal block 21. insulating support 79 raises spring 78 above the plane of the elongated contacts 19A and 19B and increases the voltage breakdown level between contacts 19A and NB. Helical spring 78 is thus in effect, compressed between terminal block 21 and movable member 18 and urges the movable member 18 against cam pin 76 to assure adequate driving torque when the switch is in the rotatable position with cam pin 76 in the V-shaped depression 74 as seen in FIG. 7. When the switch it) is actuated from the parallel position shown in FIG. 4 to the series position shown in FIG. 5, or vice versa, the slot 64- in cap 63 is engaged with the wedge-shaped end 632 on actuating member 66) and I0- tated to revolve the stub shaft and operating shaft 40. Rotation of shaft it) moves cam pin 76 from the position shown in FIGS. 2-6 wherein it bears against the raised cam portions 75, into the depressions 74 on the cam 73 as shown in FIG. 7, thereby actuating the movable member 18 in a direction axially of shaft 49 from the position shown in FIG. 6 to the position shown in FIG. 7 and from the position shown in full lines to the position shown in dotted lines in FIG. 3. Such axial actuation of movable member 18 disengages the elongated contacts 19A and 193 from the stationary contact pins 26 and removes contact pressure therebetween as shown in FIG. 7 to facilitate rotation of the movable member 18.

The snap rings 36 on stationary contact pins 26 abutting against the shoulders 33 permit only limited axial movement of pins 26 so that all contact pressure is relieved after only slight axial movement of movable members 18, and it will be appreciated that relief of all contact pressure permits actuation of switch 11% between positions with minimum torque exerted on shaft 45. Spring 78 retains cam pin 76 within the V-shaped depressions 74 to actuate the movable member 18 to the other switch position upon continued rotation of shafit 46) after contact pressure is relieved.

With cam pin '76 in the depressions 74, rotation of shaft 44 will also revolve the movable member 18 until one of the depending stops 71A or 71B thereon comes into engagement with the raised stop 72 on terminal block 21, thereby preventing further rotation of movable member 018 and assuring that the movable contacts 19A and 19B are in the desired position relative to the stationary contact pins 26. As shown in FIG. 4, stop member 71A on movable member 18 abuts against stop member 72 on terminal block 21 in the parallel position of the dualvoltage switch. Rotation of movable member 18 ninety degrees counterclockwise from the position as seen in FIG. 4 to the position shown in FIG. 5 brings stop member 71B into engagement with stop member 72 and thus assures that the movable contacts 19A and 19B are in the desired series position relative to the stationary contacts A-F. Further rotation of shaft 40 will move cam pin 76 from the position shown in FIG. 7 up the inclined sides of depressions 74 into the position shown in FIG. 6 wherein it bears against raised cam portions 75 and thus forces the movable member 18 gradually in an axial direction toward terminal block 21, thereby urging the contact pins 25 into the tubular bushings 24 and compressing the helical springs 34. Further, when the cam pin 76 rests upon the flat pontions 75 of cam 73 between the depressions 74, the desired predetermined high pressure contact is again obtained between the movable contacts 19A and 19B and the stationary contact pins 26. Contact pressures of up to sixty pounds can be obtained with the switch of the invention with only slight axial movement of movable member 13, and such high contact pressure permits the switch to continually carry the rated current of 69 amperes specified by NEMA standards for 167 kva. transformers and also permits carrying short circuit currents of twentyfive times such rated current for two seconds.

Overtravel of shafts 4t and 45 does not affect the positioning of the movable contacts 19A-19B. The stop members 71 and 72 positively position the movable contacts 19A and 193 relative to the stationary contacts A- F so that the rotational positioning of the operating shaft 15 not critical.

It will be apparent that the disclosed dual-voltage switch is much more compact than prior switches for a given transformer kva. and voltage rating and that it occupies minimum space in the transformer tank even at the higher voltage and kva ratings.

FIG. 8 is a schematic diagram of the circuit connections when the switch illustrated in FIGS. 27 is used to alternately connect two transformer winding sections in series and parallel and thus change voltage in a 2 to 1 ratio. Only four of the stationary contacts A-D are utilized. The ends A and C of the two coil sections AB and CD are connected by leads 15 to the correspondingly lettered stationary contacts of one set A, C and the ends B and D of the coil sections AB and CD are connected to correspondingly lettered stationary contacts of the other set B, D. When the movable contacts 19A and 10B are in the full line position as seen in FlG. 8, the two winding sections AB and CD are connected in parallel. When the switch is actuated to the dotted-line position, the two windings AB and CD are connected in a series circuit which may be traced from one power line lead 16, winding section AB, stationary contact B, movable metallic contact 19A, stationary contact C, and winding section CD to the other power line lead 16.

FIGS. 1-8 illustrate embodiments for changing the Voltage in whole number, or integer, multiples, for example, from 2400 to 7200 volts in a 3 to 1 ratio or from 2400 to 4800 volts in a 2 to 1 ratio. An electric utility often desires to change transformer voltages in ratios other than integers, for example, from 2400 to 7620 volts. MG. 9 is a circuit diagram of dual-voltage switching means of the invention for changing voltages in other than multiples of whole numbers and FIG. 10 illustrates an embodiment of switch means for use in the circuit of FIG. 9 wherein both a dual voltage switch having high contact pressure as disclosed in FIGS. 2-7 and a similar auxiliary, or slave, switch may be actuated manually "from the same shaft with low operating torque. Inasmuch as contact pressure is relieved between stationary and movable contacts when the main and auxiliary switches are actuated between switch positions, it will be apparent that only slight turning moment need be applied to the operating shaft. A main switch 10A and an auxiliary switch 1038, both of which are similar to the embodiment of FIGS. 2-7, are mechanically interconnected as shown in FIG. 10 to permit actuation from a single operating shaft. The ganged switches 10A and 10B are preferably mounted on brackets 11 so that the sides thereof for receiving the wire leads 115 face each other. A suitable mechanical coupling 81 interconnects the shafts 40A and 40B of the switches 10A and 10B. One switch shaft, for example, shaft 40A is mechanically connected by means not shown to stub shaft 45 in a manner similar to that illustrated in F16 2.

Main switch 10A is provided with elongated, metallic, straight movable contacts 19A and 193 in a manner identical to the embodiments of FIGS. 2-7. Auxil ary switch 10B is provided with a pair of L-shaped metallic contacts 82A and 82B insulated from each other and carried on the straight portions 60A and 69B of auxiliary sw tch 10B. L-shaped movable contact 82A of auxiliary sw tch 10B is adapted in the series position shown in full lines in FIG. 9 to electrically common stationary contacts 83 and 84 of auxiliary switch 10B, and in the parallel switch position shown in dotted lines in FIG. 9 to electrically common stationary contacts 83 and of auxiliary switch B.- Similarly L-shaped contact tBZB is adapted in the series position shown in full lines in FIG. 9 to electrically common stationary contacts $7 and 88 and in the parallel position shown in dotted lines to electrically common stationary contacts $6 and 87.

A tap 90 on winding section AB is connected by a lead to stationary contact 85 of auxiliary switch 108. A tap 91 on winding EF is connected to stationary contact 86 on auxiliary switch 1013. In the illustrated embodiment for changing from 2400 to 7620 volts, the voltage across each winding AB and GP is 2610 volts; the potential between end A of winding AB and tap 90 is 210 volts; the voltage between tap 91 and end F of winding EF is 210 volts; and the voltage across winding CD is 2400 volts.

With the main and auxiliary switches 10A and 1013 in the series position shown in full lines, the voltage across the transformer primary is 7620 volts and the three windings AB, CD, and EP are connected in series in a circuit which may be traced from one primary line lead 16, stationary contact 84 of auxiliary switch 10B, L-shaped contact 82A, stationary contact 53, winding section AB,

stationary contact B of main switch 10A, elongated contact 10A of main switch 10A, stationary contact C, coil section CD, stationary contact D, elongated contact 13 3, stationary contact E, coil section EF, stationary contact 83, L-shaped contact tiZB of auxiliary switch 103, and stationary contact 37 to the other primary line lead 16. The primary voltage will thus be 2610 plus 2400 plus 2610 equals 7620 volts.

When the actuating member 60 and operating shaft 40 are rotated by engaging the nick 64 in cap 63 with the wedge-shaped end 62 on actuating member 60, interconnected shafts 40A and 40B are revolved to operate the main and auxiliary switches 10A and 108 to the dotted line position in a manner identical to that described for the embodiment of FIGS. 2-7. Inasmuch as contact pressure is relieved during actuation of the movable contact assemblies between series and parallel positions, minimum torque is required to operate the ganged switches 10A and 108. In the parallel position of the dual voltage switching means shown in dotted lines, the 2400 volt winding CD is connected in parallel with the 2400 volt portion of winding AB between tap 90 and end B and also with the 2400 volt portion of winding EF between end B and tap 9.1. Tap W, end C of winding section CD and end E of winding section EF are commoned in a circuit which may be traced from the left hand power line lead 16 to (a) stationary contact 84, l..-shaped contact 823, and stationary contact to tap (b) stationary contact A, elongated contact 19A, stationary contact E, to end E of winding section EP; and (c) stationary contact A, elongated contact 1 3A and stationary contact C to end C of winding CD. End B of winding AB, end D of winding CD, and tap 91 are commoned in a circuit which may be traced from the right hand primary line lead 16 as seen in FIG. 9 to (a) stationary contact J1", L-shaped contact tiZA and stationary contact 86 to tap 91 on winding EF; (12) stationary contact F, movable contact 193 and stationary contact D to end D of winding CD; and (c) stationary contact F, elongated contact 193 of main switch 10A and stationary contact B to end B of winding AB.

FIG. 11 illustrates an alternative embodiment of the invention wherein the surfaces 93 on stop member 72 and the cooperating surfaces 94 on stop members 71A and 713 which engage stop member 72 are disposed at an angle to the axis of shaft 40 to cause a wiping action of movable contacts 19A and 19B across contact pins 236 as they are brought into engagement.

Although the invention has been illustrated and described with the rotatable contacts moving toward the normally spring-loaded stationary contacts to increase contact pressure at the switch positions and to remove contact pressure in moving between switch positions, it will be appreciated that the invention is not so limited and also comprehends moving normally spring-loaded contact pins toward and away from the rotatable contacts to increase and decrease contact pressure, or normally spring-loading the elongated movable contact bars and advancing them relative to fixed stationary contact pins.

While only a single embodiment of the transformer dual-voltage switch of the invention and a single embodiment of dual-voltage switching means for obtaining non-integer voltage multiples have been illustrated and described, many modifications and variations thereof will be apparent to those skilled in the art, and consequently it is intended in the appended claims tocover all such modifications and variations which are within the true spirit and scope of the invention.

1 claim:

1. An electrical switch comprising, in combination, an insulating base, a plurality of stationary metallic co ntacts in spaced apart relation on and being movable relative to said base, resilient means for urging said stationary contacts toward movement relative to said base, stop means for holding said stationary contacts in a position wherein said resilient means are loaded to a predetermined force, a metallic movable contact rotatable between a first position wherein it electrically commons a first set of said stationary contacts and a second position wherein it electrically commons a different set of said stationary contacts, means for operating said movable contact between said positions, and means including a cam follower and a camming member one of which is in fixed spacing relative to said base and the other of which is secured to said movable contact and being operable when said movable contact is at rest in said first and second positions for actuating said movable contact toward said base and against said stationary contacts with sufficient force to displace them relative to said base against said predetermined force of said resilient means, whereby high contact pressure is obtained between said movable and stationary contacts without rotation of said movable contact, said last named means actuating said movable contact away from said base to decrease the contact pressure between said movable and said stationary contacts while said movable contact is at rest in one of said positions before said movable contact is actuated by said operating means between said first and second positions.

2. An electrical switch comprising, in combination, an insulating base, a plurality of stationary metallic contacts in spaced apart relation on and being movable relative to said base, means for resiliently loading said stationary contacts against movement relative to said base, a metallic movable contact rotatable between a first position wherein it electrically commons a first set of said stationary contacts and a second position wherein it electrically commons a different set of said stationary contacts, operating means for rotating said movable contact between said first and second positions, means operable when said movable contact is at rest in said first and second positions for actuating said movable contact toward said base and with sufficient force against said stationary contacts to move them relative to said base against the loading of said resilient means, whereby high pressure contact is obtained between said movable and stationary contacts without rotation of said movable contact, and means for actuating said movable contact away from said base while it is at rest in one or" said positions to decrease said contact pressure before said operating means rotates it between said first and second positions.

3. An electrical switch comprising, in combination, an insulating base, a plurality of stationary metallic contacts in spaced apart relation on said base, a metallic movable contact rotatable between a first position wherein it electrically commons a first set of said stationary contacts and a second position wherein it electrically commons a different set of stationary contacts and also being operable toward and away from said stationary contacts, and operating means for rotating said movable contact between said first and second positions including means operable when said movable contact is at rest in said first and second positions for actuating it toward said base to increase contact pressure between said movable and stationary contacts and being operable while said movable contact is at rest in one of said positions to actuate it away from said base to decrease said contact pressure before said operating means rotates it between said first and second positions.

4. An electrical switch comprising, in combination, an insulating base, a plurality of stationary contact means carried in spaced apart relation on said base, an insulating member carrying a plurality of movable metallic contact means and being rotatable between a first position wherein said movable contact means electrically commons a first set of said stationary contact means and a second position wherein said movable metallic contact means electrically commons a different set of said stationary contact means, each one of said contact means being movable relative to the insulating member carrying it and toward the other contact means, resilient means for urging each of said one contact means to move relative to said insulating member carrying it, means for holding each of said one contact means in a position wherein said resilient means is loaded to a predetermined force, means including a cam follower in fixed spacing relative to said base and a camming surface on said rotatable member cooperating with said cam follower for actuating said rotatable member toward said base, when it is at rest in said first and second positions, and for pressing said movable contact means with sufiicient force against said stationary contact means to displace said one contact means against the loading of said resilient means and for actuating said rotatable member away from said base to decrease said contact pressure between said movable and stationary contact means while said insulating member is at rest in one of said positions before said rotatable member is rotated between said first and second positions, whereby predetermined high pressure contact is obtained between said stationary and movable contact means with minimum movement toward each other and said switch may be actuated with low torque between switch positions.

5. An electrical switch comprising, in combination, an insulating base, a plurality of stationary contacts carried in spaced apart relation on and being movable relative to said base and being arranged in two sets, resilient means for urging said stationary contacts to move relative to said base, stop means for limiting movement of said stationary contacts in a position wherein said resilient teams are loaded to a predetermined force, a member carrying a pair of movable metallic contacts and being movable relative to said base and rotatable between a first position wherein each of said movable contacts electrically commons the stationary contacts of one of said sets and a second position wherein it bridges between a pair of stationary contacts one of which is in each of said sets, means comprising cooperating members on said base and on said rotatable member for preventing rotation of said rotatable member beyond said first and second positions, means including a camming member and a cam follower one of which is in fixed spacing relative to said base and the other of which is secured to said rotatable member and being operable when said rotatable member is at rest in said first and second positions and preventing from further rotation by said cooperating me, bers for moving said rotatable member toward said base to engage said movable contacts with said stationary contacts and deflect said stationary contacts relative to said base against the force of said loaded resilient means, whereby a predetermined high pressure contact is obtained between said movable and stationary contacts with only slight movement of said rotatable member toward said base, and means for actuating said rotatable member away from said base to decrease said contact pressure between said movable and stationary contacts while said rotatable member is at rest in one of said positions before said rotatable member is rotated between said first and second positions.

6. An electrical switch comprising, in combination, an insulating base, a plurality of stationary metallic contacts in spaced apart relation on said base, a member carrying a movable metallic contact and being movable relative to said base and rotatable betw en a first position wherein said movable contact electrically commons a first set of said stationary contacts and a second position wherein said movable contacts electrically commons a different set of said stationary contacts, means comprising cooperating members on said base and on said rotatable member for preventing rotation of said rotatable member beyond said first and second positions, means operable when said'rotatable member is at rest in said first and second positions and prevented from further rotation by said cooperating members and including a cam follower in fixed spacing relative to said base and a camming sur face on said rotatable member cooperating with said earn follower for actuating said rotatable member toward said base and for pressing said movable contact with high contact pressure against said stationary contacts, said lastnamed means actuating said rotatable member away from said base to decrease said contact pressure between said movable and stationary contacts while said rotatable member is at rest in one of said positions before said rotatable member is operated between said first and second positions.

7. An electrical switch comprising, in combination, an insulating base having a plurality of spaced apart apertures therethrough, a plurality of headed stationary contact pins each of which extends through one of said apertures, a plurality of springs each of which surrounds one of said pins between the head thereon and said base, stop means engaging each of said pins and the side of said base opposite said springs for holding said pin in a position wherein said spring is loaded to a predetermmed force, said stationary contacts being arranged in sets, a member carrying a pair of movable metallic contacts and being movable toward and away from said base and rotatable between a first position wherein each of said movable contacts electrically commons the heads on the stationary contact pins of one of said sets and a second position wherein it bridges between the heads on a pair of stationary contact pins one of which is in each of said sets, means for actuating said rotatable member toward said base when it is at rest in said first and second positions to engage said movable contacts with said stationary contact pins and displace them sufficiently relative to said base against the force of said springs to disengage sa1d stop means from said base, whereby high pressure contact is obtained between said movable contacts and said pins in said first and second positions with only slight movement of said rotatable member toward said base, and means for displacing said rotatable member away from said base to decrease the contact pressure between said stationary and movable contacts while said rotatable member is at rest in one of said positions before said rotatable member is actuated between said first and second positions.

8. An electrical switch comprising, in combination, an insulating base, a plurality of stationary contacts carried in spaced apart relation on and being movable relative to said base, resilient means for urging said stationary contacts to move relative to said base, stop means for holding said stationary contacts in a position wherein said resilient means are loaded to a predetermined force, a metallic contact movable relative to said base and rotatable between a first position wherein it electrically cornmons a first set of said stationary contacts and a second position wherein it electrically commons a different set of said stationary contacts, means including a cam follower and a camming surface one of which is in fixed spacing relative to said base and the other of which is secured to said rotatable contact and being operable when said rotatable contact is at rest in said first and second positions for moving said rotatable contact toward said base and pressing it with sufficient force against said stationary contacts to displace them against the loading of said resilient means, whereby predetermined high contact pressure is obtained between said stationary and movable contacts without rotation of said movable contact and with only slight relative movement therebetween, said cam means moving said rotatable contact away from said base to decrease said contact pressure while said movable contact is at rest in one of said positions before said movable contact is actuated between said first and second positions, whereby said switch may be easily operated between switch positions.

9. A compact, high contact pressure, low operating torque electrical switch comprising, in combination, an insulating base having a plurality of spaced apart apertures therethrough, a plurality of headed stationary con- Cir tact pins each of which extends through one of said apertures, a plurality of springs each of which surrounds one of said pins between the head thereon and said base, stop means engaging each of said pins and the side of said base opposite said springs for holding said pin in a position wherein said spring is loaded to a predetermined force, an o crating shaft, a metallic contact operatively connected to said shaft and rotatable between a first position wherein it electrically commons the heads on one set of said pins and a second position wherein it bridges between the heads on a different set of pins and also being movable in a direction axially of said pins and said shaft, means including a cam follower and a camming member one of which is aifixed to said shaft and the other of which is secured to said rotatable contact and being operable when said rotatable contact is at rest in said first and second positions for actuating said rotatable contact toward said base and for pressing it with suficient force against the heads on said pins to disengage said stop means from said base, whereby high contact pressure is obtained between said pins and said rotatable contact, and means operable while said metallic rotatable contact is at rest in one of said positions when said shaft is rotated in a direction to actuate said rotatable contact etween said positions for moving said rotatable contact in a direction axially of said pins to decrease said contact pressure.

10. A compact electrical switch requiring low operating torque but having high contact pressure and relatively long creepage paths comprising, in combination, a stationary base having high surface resistivity and a plurality of spaced apart tubular housings raised above the surface thereof, a plurality of metallic contact pins each of which is slidable axially in one of said tubular housings, resilient means for urging said pins in a direction out of said housings, means for limiting movement of said pins beyond a predetermined position wherein said resilient means are normally loaded, a metallic contact rotatable between a first position wherein it electrically commons one set of said pins and a second position wherein it bridges between and electrically commons a different set of said pins and being movable in a direction axially of said pins, means for moving said rotatable contact toward said base when it is at rest in said first and second positions and for pressing it with sufiicient force against said pins to deflect them against the loading of said resilient means, whereby high contact pressure is obtained between said pins and said movable contact, said last-named means being operable while said rotatable contact is at rest in one of said positions to move said rotatable movable contact in a direction axially of said pins to decrease said contact pressure before said movable contact is rotated between switch positions.

11. An electrical switch comprising, in combination, an insulating base, a plurality of stationary contacts carried in spaced apart relation on and being movable relative to said base, resilient means for urging said stationary contacts to move relative to said base, means for holding said stationary contacts in a position wherein said resilient means is loaded to a predetermined force, an operating shaft, a member on said shaft movable axially relative thereto and carrying at least one movable metallic contact and being rotatable between a first position wherein said movable metallic contact electrically commons a first set of stationary contacts and a second position wherein said movable metallic contact electrically commons a different set of stationary contacts, a camming surface on said rotatable member having at least one depression therein, cooperating members on said base and on said rotatable member for preventing rotation of said member beyond said first and second positions, a cam follower pin on said shaft adapted to move across said camming surface, said cam pin when in said depression providing a driving connection between said shaft and said rotatable member, said cam pin riding out of said depression when said rotatable member is at rest in said first and second positions and is held against further rotation by said cooperating members and actuating said rotatable member axially of said shaft to press said movable contact against said stationary contacts and displace them relative to said base against said predetermined loading of said resilient means, said cam pin within said depression also permitting movement of said rotatable member axially of said shaft to decrease the contact pressure b tween said movable contact and said stationary contacts while said rotatable member is at rest in one of said positions before said rotatable member is actuated between said first and second positions.

12. A compact, high contact pressure, low operating torque electrical switch comprising, in combination, an insulating base, a plurality of stationary contacts mounted in spaced apart relation on said base and being movable relative to said base, resilient means for urging said stationary contacts away from said base, means for limiting movement of said stationary contacts in a direction away from said base in a predetermined position wherein said resilient means are normally loaded, a shaft rotatable about an axis transverse to said base, a member rotatably carried on and movable axially of said shaft and carrying movable metallic contact means adapted to engage said stationary contacts, said member being rotatable between first and second positions wherein said movable contact means and said stationary contacts are connected in different electrical arrangements, a cam affixed to said member and having a depression therein, a cam follower pin affixed to said shaft, second resilient means for urging said rotatable member away from said base and said cam against said cam pin, rotation of said shaft when said member is at rest in said first and second posi- :tions causing said cam pin to ride out of said depression and actuate said rotatable member axially of said shaft ,and pressing said movable contact means with sufiicient pressure into engagement with said stationary contacts to deflect said stationary contacts in a direction toward said base against the force of said first resilient means, rotation of said shaft in a direction to actuate said member between first and second positions causing said cam pin to fall into said depression to effect a driving connection between said shaft and said member and moving said member axially of said shaft while it is at rest in one of said positions under the force of said second resilient means in a direction to decrease the contact pressure between said movable contaot means and said stationary contacts.

13. 'A compact, high contact pressure, low operating torque electrical switch having relatively long creepage paths and arc-over distance-s comprising, in combination, a stationary insulating base having high surface resistivity and two sets of parallel, spaced apart tubular contact housings raised above the surface of said base, a plurality of metallic Contact pins, one being slidable axially in each of said tubular housings, means for resiliently urg ing said contact pins in a direction out of said housings, means for limiting movement of said pins out of said housings beyond a predetermined position wherein said resilient means is normally loaded, a movable member having high surface resistivity rotatable about an axis parallel to the axis of said housings and being movable relative to said base and carrying a pair of spaced apart, elongated metallic contacts adapted to engage said contact pins, said movable member being rotatable between a first position wherein each of said elongated contacts electrically commons the contact pins in one of said sets and a second position wherein said elongated contact bridges between a pair of said contact pins one of which is in each of said sets, stop means comprising cooperating members on said base and on said movable member for preventing rotation of said movable member beyond said first and second positions, and operating means for rotating said'movable member between said first and second positions, said operating means including a cam follower in fixed spacing relative to said base and a camming surface on said movable member cooperating with said cam follower for actuating said movable member towards said base and for pressing said elongated contacts against said contact pins with sufficient force to deflect said pins in a direction into said housings against the loading of said resilient means when said movable member is at rest in said first and second position and is prevented from rotating by said stop means and for actuating said movable member away from said base to disengage said movable contacts from said contact pins while said movable member is at rest in one of said positions before said movable member is actuated be tween said first and second positions.

14. A compact, high contact pressure, low operating torque electrical switch comprising, in combination, an insulating base, a plurality of stationary contacts mounted in spaced apart relation on and being movable relative to said base, resilient means for urging said stationary contacts away from said base, means for limiting movement of said stationary contacts in a direction away from said base in a predetermined position wherein said resilient means are normally loaded, a shaft rotatable about an axis transverse to said base, a member rotatably carried on and movable axially of said shaft and carrying movable metallic contact means adapted to engage said stationary contacts, said member being rotatable between first and second positions wherein said movable contact means and said stationary contacts are connected in different electrical arrangements, a camming surface on said member having a depression therein, a cam follower pin afiixed to said shaft, second resilient means for urging said member away from said base and said cam pin against said camming surface, stop means including cooperating members on said rotatable member and said base for preventing movement of said rotatable member beyond said first and second positions, rotation of said shaft in a direction to actuate said rotatable member between first and second positions causing said cam pin to fall into said depression and effect a driving connection between said shaft and said rotatable memher and moving said rotatable member axially in a direction to decrease the contact pressure between said movable contact means and said stationary contacts while said rotatable member is at rest in said one of said first and second positions, rotation of said shaft after said stop means has prevented movement of said rotatable member beyond one of said positions causing said cam pin to ride out of said depression and actuate said rotatable member toward said base and press-said movable contact means with sufficient force against said stationary contacts to deflect them relative to said base against the force of said first resilient means while said rotatable member is a rest in said one of said positions, whereby high pressure contact is obtained when :said switch is in said first and second positions and said switch is operated with low torque between switch positions.

15. A compact, high contact pressure, low operating torque electrical switch having relatively long creepage paths comprising, in combination, a stationary insulating base having high surface resistivity, a plurality of spaced apart, tubular contact housings on said base raised above the surface thereof, a plurality of metallic stationary contact pins slidable axially in said housings, means for resiliently urging said contact pins in a direction out of said housings, means for limiting movement of said pins beyond a predetermined position wherein said resilient means are normally loaded, a shaft co-axial of said housings, a member of relatively high surface resistivity, operatively connected to said shaft and carrying a pair of spaced apart metallic contacts and being rotatable between first and second positions wherein said movable contacts bridge between different pairs of said contact pins, stop means comprising cooperating members on said base and on said rotatable member for pre: venting rotation of said rotatable member beyond said first and second positions, means including a cam follower secured to said shaft and a camming surface on said rotatable member cooperating with said cam follower and being operable in response to rotation of said shaft when said rotatable member is at rest in said first and second positions and is prevented from further rotation by said stop means for moving said rotatable member toward said base and for pressing said movable contacts against said pins to deflect them in a direction into said housing against the force of said resilient means, whereby high pressure contact is obtained between said movable contacts and said pins with only slight movement of said rotatable member, said camming means also being adapted in response to rotation of said shaft in a direction to operate said rotatable member between first and second positions to actuate said rotatable member away from said base and decrease the contact pressure between said movable contacts and said contact pins while said rotatable member is at rest in one of said positions.

16. An electrical switch comprising, in combination, a plurality of spaced apart stationary contacts, an operating shaft, a member carrying a movable metallic. contact and having an axial aperture receiving said shaft and being reciprocable axially of said shaft to move said movable contact toward and away from said stationary contacts and being rotatable with said shaft between a first position wherein said movable contact electrically commons a first set of said stationary contacts and a second position wherein said movable contact electrically commons a different set of said stationary contacts, means including a camming surface on said member and a cam follower affixed to said shaft and adapted to move across said camming surface for operating said member between said first and second positions, said last-named means being operable when said member is at rest in said first and second positions to move said member axially of said shaft toward said stationary contacts to increase the contact pressure between said movable and stationary contacts and also being operable while said member is at rest in one of said positions to move said member axially of said shaft away from said stationary contacts to decrease the contact pressure between said stationary and movable contacts before said member is rotated between said positions.

17. An electrical switch comprising, in combination, a plurality of spaced apart stationary metallic contacts, a metallic contact movable between a first position wherein it electrically commons a first set of said stationary contacts and a .second position wherein it electrically commons a different set of said stationary contracts, said metallic contact also being movable in a direction toward and away from said stationary contacts, means for operating said movable contact between said first and second positions, and means including a cam follower and a camming member one of which is in fixed spacing relative to said stationary contacts and the other is secured to said movable contact and being operable only after said movable contact is at rest in said first or said second position for actuating said movable contact toward said stationary contacts and increasing the contact pressure between said stationary and movable contacts, said last-named means also being operable to actuate said movable contact away from said stationary contacts and decrease the contact pressure between said stationary and movable contacts while said movable contact is at rest in one of said positions before said movable contact is operated between said positions.

18. An electrical switch comprising, in combination, a plurality of spaced apart metallic, stationary contact means, metallic movable contact means, resilient means for normally loading one of said contact means against movement so that a predetermined force is required to displace it, said movable contact means being operable between a first position wherein it electrically commons a first set of said stationary contact means and a second position wherein it electrically commons a different set of said stationary contact means, means for operating said movable contact means between said first and second positions, said movable contact means and said stationary contact means being relatively movable toward and away from each other, and means including a cam follower fixed in spaced relation to said one of said contact means and a camrning member secured to the other of said contact means and being operable when said movable con tact means is at rest in said first and second positions for relatively moving said stationary and movable contact means in a direction to increase the contact pressure therebetween and a sutficient distance to displace said one contact means against the force of said resilient means and being operable when said movable contact means is at rest in one of said positions to relatively move said stationary and movable contact means in a direction to decrease the contact pressure therebetween until said one contact means is again normally loaded by said resilient means before said movable contact means is operated between said positions.

References Cited by the Examiner UNITED STATES PATENTS 71,158 11/67 Gardiner. 913,080 2/09 Weman. 1,761,435 6/30 Douglas 200-4 2,4223 3 9 6/47 Christie. 2,470,625 5/49 Kuhn.

BERNARD GILHEANY, Primary Examiner. 

1. AN ELECTRICAL SWITCH COMPRISING, IN COMBINATION, AN INSULATING BASE, A PLURALITY OF STATIONARY METALLIC CONTACTS IN SPACED APART RELATION ON AND BEING MOVABLE RELATIVE TO SAID BASE, RESILIENT MEANS FOR URGING SAID STATIONARY CONTACTS TOWARD MOVEMENT RELATIVE TO SAID BASE, STOP MEANS FOR HOLDING SAID STATIONARY CONTACTS IN A POSITION WHEREIN SAID RESILIENT MEANS ARE LLADED TO A PREDETERMINED FORCE, A METALLIC MOVABLE CONTACT ROTATABLE BETWEEN A FIRST POSITION WHEREIN IT ELECTRICALLY COMMONS A FIRST SET OF SAID STATIONARY CONTACTS AND A SECOND POSITION WHEREIN IT ELECTRICALLY COMMONS A DIFFERENT SET OF SAID STATIONARY CONTACTS, MEANS FOR OPERATING SAID MOVABLE CONTACT BETWEEN SAID POSITIONS, AND MEANS INCLUDING A CAM FOLLOWER AND A CAMMING MEMBER ONE OF WHICH IS IN FIXED SPACING RELATIVE TO SAID BASE AND THE OTHER OF WHICH IS SECURED TO SAID MOVABLE CONTACT AND BEING OPERABLE WHEN SAID MOVABLE CONTACT IS AT REST IN SAID FIRST AND SECOND POSITIONS FOR ACTUATING SAID MOVABLE CONTACT TOWARD SAID BASE AND AGAINST THIS STATIONARY CONTACTS WITH SUFFICIENT FORCE TO DISPLACE THEM RELATIVE TO SAID BASE AGAINST SAID PREDETERMINED FORCE OF SAID RESILIENT MEANS, WHEREBY HIGH CONTACT PRESSURE IS OBTAINED BETWEEN SAID MOVABLE AND STATIONARY CONTACTS WITHOUT ROTATION OF SAID MOVABLE CONTACT, SAID LAST NAMED MEANS ACTUATING SAID MOVABLE CONTACT AWAY FROM SAID BASE TO DECREASE THE CONTACT PRESSURE BETWEEN SAID MOVABLE AND SAID STATIONARY CONTACTS WHILE SAID MOVABLE CONTACT IS AT REST IN ONE OF SAID POSITIONS BEFORE SAID MOVABLE CONTACT IS ACTUATED BY SAID OPERATING MEANS BETWEEN SAID FIRST AND SECOND POSITIONS. 